Wave movements in oceans and large lakes constitute an important source of energy which can be utilized by harvesting energy from the waves by means of wave power assemblies, also called wave energy converters, which are positioned or anchored at locations with suitable wave conditions.
A number of different types of wave energy converters for harvesting and converting wave energy into electrical power are previously known. One previously known type of wave energy converter is based on relative movement between, on the one hand, a buoyant body and a thereto attached so-called acceleration tube, and, on the other hand, a working piston reciprocable in the acceleration tube, wherein the relative movement is caused by wave movements in the body of water where the wave energy converter is anchored by means of one or several mooring lines for harvesting wave energy. The movement of the working piston can be used for driving, for example, a pump assembly, such as a double acting hydraulic pump or a hose pump, a hydraulic motor and/or a hydraulic turbine of an energy conversion system, which is disposed inside or adjacent to the buoyant body for producing electricity which can be transferred to an energy storage or electrical grid.
A problem that may arise with previously known wave energy converters having an acceleration tube with a working cylinder and a working piston reciprocable in the working cylinder is that the working piston gradually shifts away from its optimum operating range in the working cylinder, so that the mean vertical position of the working piston is no longer centered at the middle of the working cylinder, as viewed in the longitudinal direction thereof, but is displaced downward or upward in the acceleration tube. Such a shift or displacement of the operating range of the working piston may lead to a decreased efficiency of the wave energy converter and also cause other operational disturbances, which is of course not desirable.
Another problem with previously known wave energy converters having an acceleration tube and a hydraulic pump driven by the reciprocating movement of the working piston relative to the acceleration tube has turned out to be that a growth of barnacles and other marine organisms can appear if a piston rod of the hydraulic pump remains extended and exposed to water for a longer period of time when the wave energy converter is not operating, e.g. during light winds or other operational interruptions. Such growth of e.g. barnacles on a piston rod is undesired, since the growth may lead to operational disturbances in the wave energy converter and furthermore is difficult and time-consuming to remove.
A further problem with previously known wave energy converters having an acceleration tube and a hydraulic pump driven by the reciprocating movement of the working piston relative to the acceleration tube is that the hydraulic pump and its associated hydraulic system may give rise to a risk of leakage of hydraulic fluid to the body of water in which the wave energy converter is placed, both in the event of breakdowns and in connection with servicing or replacement of different components of the hydraulic pump and/or the hydraulic system. Such leakage of hydraulic fluid is of course not desired.
Additional problems solved by the present invention will become evident from the following description.